Envelope tracking amplifier circuit

ABSTRACT

An envelope tracking (ET) amplifier circuit is provided. The ET amplifier circuit includes an amplifier circuit configured to amplify a radio frequency (RF) signal based on an ET modulated voltage. The ET modulated voltage corresponds to a time-variant voltage envelope, which can be misaligned from a time-variant signal envelope of the RF signal due to inherent temporal delay in the ET amplifier circuit. As a result, the amplifier circuit may suffer degraded linearity performance. In this regard, a voltage processing circuit is provided in the ET amplifier circuit and configured to operate in a low-bandwidth mode and a high-bandwidth mode. In the high-bandwidth mode, the voltage processing circuit is configured to cause the ET modulated voltage to be modified to help improve delay tolerance of the ET amplifier circuit. As a result, it may be possible to reduce linearity degradation of the amplifier circuit to a predetermined threshold.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/691,454, filed on Jun. 28, 2018, which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The technology of the disclosure relates generally to envelope tracking (ET) power management in wireless communication devices.

BACKGROUND

Mobile communication devices have become increasingly common in current society. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from being pure communication tools into sophisticated mobile multimedia centers that enable enhanced user experiences.

The redefined user experience requires higher data rates offered by wireless communication technologies, such as long-term evolution (LTE). To achieve the higher data rates in mobile communication devices, sophisticated power amplifiers (PAs) may be employed to increase output power of radio frequency (RF) signals (e.g., maintaining sufficient energy per bit) communicated by mobile communication devices. However, the increased output power of RF signals can lead to increased power consumption and thermal dissipation in mobile communication devices, thus compromising overall performance and user experiences.

Envelope tracking is a power management technology designed to improve efficiency levels of PAs to help reduce power consumption and thermal dissipation in mobile communication devices. As the name suggests, envelope tracking employs a system that keeps track of the amplitude envelope of the RF signals communicated by mobile communication devices. The envelope tracking system constantly adjusts supply voltage applied to the PAs to ensure that the PAs are operating at a higher efficiency for a given instantaneous output power requirement of the RF signals.

However, the envelope tracking system can only maintain good linearity and high efficiency up to an inherent bandwidth limit. In the advent of fifth-generation new radio (5G-NR) technology, the RF signals may be modulated with a higher bandwidth (e.g., >100 MHz) than the inherent bandwidth limit of the envelope tracking system, thus reducing linearity and efficiency of the envelope tracking system. As such, it may be desirable to improve linearity and efficiency of the envelope tracking system to support the 5G-NR technology.

SUMMARY

Aspects disclosed in the detailed description include an envelope tracking (ET) amplifier circuit. The ET amplifier circuit includes an amplifier circuit configured to amplify a radio frequency (RF) signal based on an ET modulated voltage. The ET modulated voltage corresponds to a time-variant voltage envelope, which can be misaligned from a time-variant signal envelope of the RF signal due to inherent temporal delay in the ET amplifier circuit. As a result, the amplifier circuit may suffer degraded linearity performance. In this regard, a voltage processing circuit is provided in the ET amplifier circuit and configured to operate in a low-bandwidth mode (e.g., modulation bandwidth≤60 MHz) and a high-bandwidth mode (e.g., modulation bandwidth>60 MHz). In the high-bandwidth mode, the voltage processing circuit is configured to cause the ET modulated voltage to be modified to help improve delay tolerance of the ET amplifier circuit. As a result, it may be possible to reduce linearity degradation of the amplifier circuit to a predetermined threshold.

In one aspect, an ET amplifier circuit is provided. The ET amplifier circuit includes an ET voltage circuit configured to generate an ET modulated voltage corresponding to a time-variant voltage envelope. The ET amplifier circuit also includes a signal processing circuit configured to generate an RF signal corresponding to a time-variant signal envelope. The ET amplifier circuit also includes an amplifier circuit configured to amplify the RF signal based on the ET modulated voltage. The ET amplifier circuit also includes a voltage processing circuit configured to operate in a low-bandwidth mode and a high-bandwidth mode. The voltage processing circuit is further configured to cause the ET voltage circuit to modify the ET modulated voltage in the high-bandwidth mode to reduce linearity degradation caused by a temporal misalignment between the time-variant voltage envelope and the time-variant signal envelope at the amplifier circuit to a predetermined threshold.

Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

FIG. 1A is a schematic diagram of an exemplary existing envelope tracking (ET) amplifier circuit that can experience degraded overall linearity performance as a result of inherent processing and/or propagation delays of the existing ET amplifier circuit;

FIG. 1B is a graphic diagram providing an exemplary illustration of a temporal misalignment between a time-variant voltage envelope and a time-variant signal envelope that can occur in the existing ET amplifier circuit of FIG. 1A;

FIG. 1C is a graphic diagram providing an exemplary illustration of how a temporal delay can affect adjacent channel leakage ratio (ACLR) of an amplifier circuit in the existing ET amplifier circuit of FIG. 1A;

FIG. 2 is a schematic diagram of an exemplary ET amplifier circuit configured according to an embodiment of the present disclosure to reduce linearity degradation by improving delay tolerance of the ET amplifier circuit;

FIG. 3 is a schematic diagram of an exemplary digital voltage processing circuit configured according to one embodiment of the present disclosure and can be included in the ET amplifier circuit of FIG. 2;

FIG. 4A is a graphic diagram providing an exemplary illustration of generating a number of time-variant modified digital voltage amplitudes based on a constant voltage offset;

FIG. 4B is a graphic diagram providing an exemplary illustration of generating a number of time-variant modified digital voltage amplitudes based on a number of variable voltage offsets;

FIG. 5 is a schematic diagram of an exemplary digital voltage processing circuit configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit of FIG. 2;

FIG. 6 is a schematic diagram of an exemplary digital voltage processing circuit configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit of FIG. 2; and

FIG. 7 is a schematic diagram of an exemplary digital voltage processing circuit configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit of FIG. 2.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Aspects disclosed in the detailed description include an envelope tracking (ET) amplifier circuit. The ET amplifier circuit includes an amplifier circuit configured to amplify a radio frequency (RF) signal based on an ET modulated voltage. The ET modulated voltage corresponds to a time-variant voltage envelope, which can be misaligned from a time-variant signal envelope of the RF signal due to inherent temporal delay in the ET amplifier circuit. As a result, the amplifier circuit may suffer degraded linearity performance. In this regard, a voltage processing circuit is provided in the ET amplifier circuit and configured to operate in a low-bandwidth mode (e.g., modulation bandwidth≤60 MHz) and a high-bandwidth mode (e.g., modulation bandwidth>60 MHz). In the high-bandwidth mode, the voltage processing circuit is configured to cause the ET modulated voltage to be modified to help improve delay tolerance of the ET amplifier circuit. As a result, it may be possible to reduce linearity degradation of the amplifier circuit to a predetermined threshold.

Before discussing an ET amplifier circuit of the present disclosure, a brief overview of an existing ET amplifier circuit that may experience degraded overall linearity performance as a result of inherent temporal delay associated with the existing ET amplifier circuit is first provided with reference to FIGS. 1A-1C. The discussion of specific exemplary aspects of the ET amplifier circuit of the present disclosure starts below with reference to FIG. 2.

FIG. 1A is a schematic diagram of an exemplary existing ET amplifier circuit 10 that can experience degraded overall linearity performance as a result of inherent processing and/or propagation delays of the existing ET amplifier circuit 10. The existing ET amplifier circuit 10 includes a 106ssing circuit 12, an ET voltage circuit 14, and an amplifier circuit 16. The signal processing circuit 12 receives a digital signal 18 that includes a number of time-variant digital signal amplitudes 20 representing a time-variant digital signal envelope 22. The phrase “time-variant” is used hereinafter to refer to a parameter (e.g., amplitude, voltage, power, etc.) that changes (e.g., increases or decreases) over time.

The signal processing circuit 12 is configured to convert the digital signal 18 into an RF signal 24 having a time-variant signal envelope 26 formed based on the time-variant digital signal envelope 22. In this regard, the time-variant digital signal envelope 22, which is defined by the time-variant digital signal amplitudes 20, can be seen as a digital representation of the time-variant signal envelope 26.

The digital signal 18 may be modulated to include a digital in-phase signal 281, which has a number of time-variant in-phase amplitudes I, and a digital quadrature signal 28Q, which has a number of time-variant quadrature amplitudes Q. In this regard, the time-variant digital signal amplitudes 20 of the digital signal 18 can be expressed as √{square root over (I²+Q²)}.

The existing ET amplifier circuit 10 includes a mixer 30 that combines the time-variant digital signal amplitudes 20 with a digital voltage reference signal 32 to generate a digital target voltage reference signal 34. In this regard, the digital target voltage reference signal 34 is associated with the time-variant digital signal envelope 22 and, therefore, the time-variant digital signal amplitudes 20.

The existing ET amplifier circuit 10 includes lookup table (LUT) circuitry 36 (denoted as “LUT” in FIG. 1A), which may store a number of predetermined target voltage amplitude values corresponding to the time-variant digital signal amplitudes 20. In this regard, the LUT circuitry 36 converts the time-variant digital signal amplitudes 20 into a number of time-variant digital target voltage amplitudes 38 and associates the time-variant digital target voltage amplitudes 38 with a digital target voltage signal 40. As a result of such digital conversion, the time-variant digital target voltage amplitudes 38 may be distorted. For example, the LUT circuitry 36 can be non-strictly monotonic. As a result, a digital target voltage amplitude among the time-variant digital target voltage amplitudes 38 can become higher or lower than a corresponding digital signal amplitude among the time-variant digital signal amplitudes 20.

The existing ET amplifier circuit 10 includes a voltage digital-to-analog converter (DAC) 42 configured to convert the digital target voltage signal 40 into a target voltage signal 44 having a time-variant target voltage envelope 46 formed based on the time-variant digital target voltage amplitudes 38. The DAC 42 is configured to provide the target voltage signal 44 to the ET voltage circuit 14.

The ET voltage circuit 14 receives the target voltage signal 44 having the time-variant target voltage envelope 46. The time-variant target voltage envelope 46 may represent a time-variant target voltage V_(TARGET) for the ET voltage circuit 14. The ET voltage circuit 14 is configured to generate an ET modulated voltage V_(CC) having a time-variant voltage envelope 48 that tracks the time-variant target voltage envelope 46. The ET modulated voltage V_(CC) is a time-variant ET modulated voltage formed based on the time-variant target voltage V_(TARGET). Accordingly, the ET modulated voltage V_(CC) tracks the time-variant target voltage V_(TARGET).

The amplifier circuit 16 is coupled to the signal processing circuit 12 to receive the RF signal 24 having the time-variant signal envelope 26. The amplifier circuit 16 is also coupled to the ET voltage circuit 14 to receive the ET modulated voltage V_(CC) corresponding to the time-variant voltage envelope 48. The amplifier circuit 16 is configured to amplify the RF signal 24 based on the ET modulated voltage V_(CC). In this regard, to maintain linearity and efficiency in the amplifier circuit 16, the time-variant voltage envelope 48 of the ET modulated voltage V_(CC) needs to align closely with the time-variant signal envelope 26 at the amplifier circuit 16.

However, the signal processing circuit 12, the LUT circuitry 36, the DAC 42, and the ET voltage circuit 14 may each incur processing/propagation delays. In addition, the amplifier circuit 16 may be a multi-stage amplifier including a driver stage 50 and an output stage 52 that also incur respective processing/propagation delays. As a result, the time-variant voltage envelope 48 may be out of alignment with the time-variant signal envelope 26 at the amplifier circuit 16.

In this regard, FIG. 1B is a graphic diagram providing an exemplary illustration of a temporal misalignment between the time-variant voltage envelope 48 and the time-variant signal envelope 26 of FIG. 1A. Elements of FIG. 1A are referenced in conjunction with FIG. 1B and will not be re-described herein.

If the time-variant signal envelope 26 and the time-variant voltage envelope 48 are perfectly aligned, an instantaneous amplitude of the RF signal 24 (not shown), which is represented by a voltage V_(S), would substantially equal the ET modulated voltage V_(CC) at time t_(x). However, as shown in FIG. 1B, the time-variant signal envelope 26 lags behind the time-variant voltage envelope 48 by a temporal delay Δt. As such, at time t_(x), the amplifier circuit 16 (not shown) receives a lower ET modulated voltage V′_(CC), instead of the ET modulated voltage V_(CC). In this regard, the time-variant voltage envelope 48 deviates from the time-variant signal envelope 26 by a voltage differential Δv at time t_(x). Consequently, the amplifier circuit 16 may suffer degraded linearity performance.

In a non-limiting example, the linearity performance of the amplifier circuit 16 can be measured by adjacent channel leakage ratio (ACLR). The ACLR represents a ratio between in-band power and out-of-band leakage power. In this regard, a higher ACLR indicates a better linearity performance of the amplifier circuit 16. FIG. 1C is a graphic diagram providing an exemplary illustration of how the temporal delay Δt of FIG. 1B can affect the ACLR of the amplifier circuit 16 of FIG. 1A. Elements of FIGS. 1A and 1B are referenced in conjunction with FIG. 1C and will not be re-described herein.

FIG. 1C includes a first ACLR curve 54 and a second ACLR curve 56. In a non-limiting example, the first ACLR curve 54 corresponds to an RF signal (e.g., the RF signal 24) modulated at 100 MHz bandwidth and the second ACLR curve 56 corresponds to an RF signal (e.g., the RF signal 24) modulated at 60 MHz bandwidth. As shown in FIG. 1C, the first ACLR curve 54 has a steeper slope compared to the second ACLR curve 56. In this regard, to achieve −32 dB ACLR, for example, the existing ET amplifier circuit 10 is confined to a delay budget of approximately 1.0 nanosecond (ns) when the RF signal 24 is modulated at 100 MHz bandwidth. In contrast, the existing ET amplifier circuit 10 would be subject to a more relaxed delay budget of approximately 1.3 ns for the same −32 dB ACLR when the RF signal 24 is modulated at 60 MHz bandwidth.

Notably, the RF signal 24 may be a long-term evolution (LTE) signal, which is typically modulated at up to 60 MHz modulation bandwidth or a fifth-generation new-radio (5G-NR) signal that is often modulated at more than 100 MHz modulation bandwidth. In this regard, the existing ET amplifier circuit 10 must adhere to a more stringent delay budget to achieve a desirable ACLR at the amplifier circuit 16 for communicating the RF signal 24 in a 5G-NR system.

With reference back to FIG. 1B, to mitigate linearity degradation and achieve the desirable ACLR at the amplifier circuit 16, it is necessary to reduce the temporal delay Δt between the time-variant voltage envelope 48 and the time-variant signal envelope 26. However, it may be difficult to do so adequately in the existing ET amplifier circuit 10 to satisfy the more stringent delay budget required for communicating a 5G-NR signal modulated at the higher modulation bandwidth (e.g., >100 MHz). As such, it may be desirable to improve delay tolerance of the existing ET amplifier circuit 10 to reduce linearity degradation caused by temporal misalignment between the time-variant voltage envelope 48 and the time-variant signal envelope 26.

In this regard, FIG. 2 is a schematic diagram of an exemplary ET amplifier circuit 58 configured according an embodiment of the present disclosure to reduce linearity degradation by improving delay tolerance of the ET amplifier circuit 58. As discussed below in detail, the ET amplifier circuit 58 can be configured to dynamically reduce the voltage differential Δv in FIG. 1B independent of whether the temporal delay Δt in FIG. 1B is reduced. Further, the ET amplifier circuit 58 may also be configured to reduce gain sensitivity in a coupled amplifier circuit to the voltage differential Δv independent of whether the temporal delay Δt in FIG. 1B is reduced. As such, the ET amplifier circuit 58 may be able to reduce linearity degradation to a predefined threshold even if the temporal delay Δt is not reduced. Accordingly, the ET amplifier circuit 58 becomes more delay tolerant, particularly for communicating a 5G-NR signal modulated at a bandwidth in excess of 100 MHz.

The ET amplifier circuit includes an ET voltage circuit 60, which may be functionally equivalent to the ET voltage circuit 14 of FIG. 1A. The ET voltage circuit 60 is configured to generate an ET modulated voltage V_(CC) based on a target voltage signal 62. The target voltage signal 62 corresponds to a time-variant target voltage envelope 64 and the ET modulated voltage V_(CC) corresponds to a time-variant voltage envelope 66 configured to track the time-variant target voltage envelope 64. In this regard, it may be possible to modify the time-variant voltage envelope 66, and therefore the ET modulated voltage V_(CC), by modifying the time-variant target voltage envelope 64.

The ET amplifier circuit 58 includes a signal processing circuit 68, which may be functionally equivalent to the signal processing circuit 12 of FIG. 1A. The signal processing circuit 68 is configured to receive a digital signal 70 and convert the digital signal 70 into an RF signal 72. The signal processing circuit 68 may include digital pre-distortion (DPD) circuitry (not shown) to digitally pre-distort the digital signal 70 prior to converting the digital signal 70 into the RF signal 72. The digital signal 70 may be modulated to include a digital in-phase signal 74I, which has a number of time-variant in-phase amplitudes I, and a digital quadrature signal 74Q, which has a number of time-variant quadrature amplitudes Q. Accordingly, the digital signal 70 corresponds to a number of time-variant digital signal amplitudes 76. Each of the time-variant digital signal amplitudes 76 can be expressed as √{square root over (I²+Q²)}. By converting the digital signal 70 into the RF signal 72, the RF signal 72 is associated with a time-variant signal envelope 78 formed based on the time-variant digital signal amplitudes 76.

The ET amplifier circuit 58 includes an amplifier circuit 80, which may be functionally equivalent to the amplifier circuit 16 of FIG. 1A. The amplifier circuit 80 is configured to amplify the RF signal 72 based on the ET modulated voltage V_(CC).

Similar to the existing ET amplifier circuit 10 of FIG. 1A, the ET amplifier circuit 58 may cause the time-variant voltage envelope 66 to misalign with the time-variant signal envelope 78 at the amplifier circuit 80 due to inherent temporal delays. In a non-limiting example, the amplifier circuit 80 can include a driver stage 82 and an output stage 84. In this regard, the time-variant voltage envelope 66 may be further misaligned with the time-variant signal envelope 78 at the output stage 84. According to previous discussions in FIG. 1B, the misalignment between the time-variant voltage envelope 66 and the time-variant signal envelope 78 can constantly cause the voltage differential Δv at the amplifier circuit 80. As a result, the amplifier circuit 80 may suffer linearity degradation (e.g., degraded ACLR), particularly when the RF signal 72 is modulated with a high-bandwidth in excess of 100 MHz.

In this regard, the ET amplifier circuit 58 is configured to include a voltage processing circuit 86. The voltage processing circuit 86 may operate in a low-bandwidth mode and a high-bandwidth mode. In a non-limiting example, the voltage processing circuit 86 operates in the low-bandwidth mode when the RF signal 72 is modulated with less than or equal to 60 MHz (≤60 MHz) bandwidth and in the high-bandwidth mode when the RF signal 72 is modulated with more than 60 MHz (>60 MHz) bandwidth.

In the high-bandwidth mode, the voltage processing circuit 86 can be configured to cause the ET voltage circuit 60 to modify the ET modulated voltage V_(CC) to reduce the voltage differential Δv (as shown in FIG. 1B) between the time-variant voltage envelope 66 and the time-variant signal envelope 78. As a result, it may be possible to improve delay tolerance of the ET amplifier circuit 58, thus helping to reduce the linearity degradation at the amplifier circuit 80 to a predetermined threshold (e.g., a predetermined ACLR).

In contrast, in the low-bandwidth mode, the voltage processing circuit 86 may be configured not to cause the ET voltage circuit 60 to modify the ET modulated voltage V_(CC). The ET amplifier circuit 58 may include a control circuit 88, which can be a microprocessor or a digital signal processor (DSP), for example. The control circuit 88 may be configured to control the voltage processing circuit 86 to operate in the high-bandwidth mode and the low-bandwidth mode via a first control signal 90 and a second control signal 92, respectively. In this regard, it may be possible to flexibly and dynamically toggle the ET amplifier circuit 58 between the low-bandwidth mode and the high-bandwidth mode.

The voltage processing circuit 86 includes a digital voltage processing circuit 94 and a DAC 96. The digital voltage processing circuit 94 is configured to receive the time-variant digital signal amplitudes 76 and generate a digital target voltage signal 98. In the low-bandwidth mode, the digital voltage processing circuit 94 generates the digital target voltage signal 98 corresponding to a number of time-variant digital target voltage amplitudes 100. Subsequently, the DAC 96 converts the digital target voltage signal 98 into the target voltage signal 62. Accordingly, the time-variant target voltage envelope 64 is formed based on, and thus tracking, the time-variant digital target voltage amplitudes 100.

In the high-bandwidth mode, the digital voltage processing circuit 94 generates the digital target voltage signal 98 corresponding to a number of time-variant modified digital target voltage amplitudes 102. Subsequently, the DAC 96 converts the digital target voltage signal 98 into the target voltage signal 62. Accordingly, the time-variant target voltage envelope 64 is formed based on, and thus tracking, the time-variant modified digital target voltage amplitudes 102. Given that the time-variant voltage envelope 66 tracks the time-variant target voltage envelope 64, the time-variant modified digital target voltage amplitudes 102 can cause the ET modulated voltage V_(CC) to be modified accordingly. Further, since the time-variant signal envelope 78 and the time-variant voltage envelope 66 are both formed based on the time-variant digital signal amplitudes 76, it may be possible to reduce the voltage differential Δv between the time-variant voltage envelope 66 and the time-variant signal envelope 78 by modifying the ET modulated voltage V_(CC). As a result, it may be possible to improve delay tolerance of the ET amplifier circuit 58, which can lead to improvement in linearity performance (e.g., ACLR) of the amplifier circuit 80.

In addition to improving delay tolerance of the ET amplifier circuit 58, it may also be beneficial to further reduce the temporal delay Δt (as shown in FIG. 1B) between the time-variant voltage envelope 66 and the time-variant signal envelope 78. In this regard, the voltage processing circuit 86 may include delay adjustment circuitry 104 (denoted as “Delay Adj.” in FIG. 2) to help reduce the temporal delay Δt between the time-variant voltage envelope 66 and the time-variant signal envelope 78. The signal processing circuit 68 may also include delay adjustment circuitry 106 for the same purpose. Furthermore, the voltage processing circuit 86 can include voltage memory digital pre-distortion (mDPD) circuitry 108. The voltage mDPD circuitry 108 can be configured to digitally pre-distort the digital target voltage signal 98 to help compensate for memory nonlinearity distortion in the ET voltage circuit 60.

The digital voltage processing circuit 94 may be configured based on a number of embodiments, which are discussed next. FIG. 3 is a schematic diagram of an exemplary digital voltage processing circuit 94A configured according to one embodiment of the present disclosure and can be included in the ET amplifier circuit 58 of FIG. 2 as the digital voltage processing circuit 94. Common elements between FIGS. 2 and 3 are shown therein with common element numbers and will not be re-described herein.

The digital voltage processing circuit 94A includes a mixer 110 configured to combine the time-variant digital signal amplitudes 76 with a digital voltage reference signal 112 to generate a digital target voltage reference signal 114. Accordingly, the digital target voltage reference signal 114 corresponds to the time-variant digital signal amplitudes 76, which can be represented by time-variant voltages V_(IN).

The digital voltage processing circuit 94A includes low-bandwidth LUT circuitry 116 (denoted as “LBW LUT Circuitry”) and high-bandwidth LUT circuitry 118 (denoted as “HBW LUT Circuitry”). Both the low-bandwidth LUT circuitry 116 and the high-bandwidth LUT circuitry 118 are configured to receive the digital target voltage reference signal 114 associated with the time-variant digital signal amplitudes 76. The low-bandwidth LUT circuitry 116 is further configured to generate the digital target voltage signal 98 corresponding to the time-variant digital target voltage amplitudes 100. The high-bandwidth LUT circuitry 118 is further configured to generate the digital target voltage signal 98 corresponding to the time-variant modified digital target voltage amplitudes 102.

The digital voltage processing circuit 94A includes a multiplexer 120 coupled to the low-bandwidth LUT circuitry 116 and the high-bandwidth LUT circuitry 118. The control circuit 88 (not shown) may control the multiplexer 120 to output the digital target voltage signal 98 having the time-variant modified digital target voltage amplitudes 102 in the high-bandwidth mode via the first control signal 90. The control circuit 88 may also control the multiplexer 120 to output the digital target voltage signal 98 having the time-variant digital target voltage amplitudes 100 in the low-bandwidth mode via the second control signal 92.

The low-bandwidth LUT circuitry 116 may include a low-bandwidth LUT configured to correlate the time-variant digital target voltage amplitudes 100 with the time-variant digital signal amplitudes 76. Likewise, the high-bandwidth LUT circuitry 118 may include a high-bandwidth LUT configured to correlate the time-variant modified digital target voltage amplitudes 102 with the time-variant digital signal amplitudes 76. The time-variant modified digital target voltage amplitudes 102 stored in the high-bandwidth LUT may be determined based on the time-variant digital target voltage amplitudes 100 stored in the low-bandwidth LUT, as explained next in FIGS. 4A and 4B.

FIG. 4A is a graphic diagram providing an exemplary illustrating of generating the time-variant modified digital target voltage amplitudes 102 based on a constant voltage offset V_(OFFSET). FIG. 4A includes a first curve 122 representing a correlation between the time-variant digital signal amplitudes 76 and the time-variant digital target voltage amplitudes 100. FIG. 4A also includes a second curve 124 representing a correlation between the time-variant digital signal amplitudes 76 and the time-variant modified digital target voltage amplitudes 102. The second curve 124 is parallel to the first curve 122, which indicates that the time-variant modified digital target voltage amplitudes 102 can be generated by adding the constant voltage offset V_(OFFSET) to the time-variant digital target voltage amplitudes 100. Notably, the time-variant digital target voltage amplitudes 100 and the time-variant modified digital target voltage amplitudes 102 may conform to a common digital amplitude ceiling 126, which may equal to 5.5 volts for example. It may also be possible to apply soft clipping to the time-variant digital target voltage amplitudes 100 and the time-variant modified digital target voltage amplitudes 102 in a region near the common digital amplitude ceiling 126 and/or in a region near zero.

FIG. 4B is a graphic diagram providing an exemplary illustration of generating the time-variant modified digital target voltage amplitudes 102 based on a number of variable voltage offsets V_(OFFSET-1)-V_(OFFSET-N). FIG. 4B includes a first curve 128 representing a correlation between the time-variant digital signal amplitudes 76 and the time-variant digital target voltage amplitudes 100. FIG. 4B also includes a second curve 130 representing a correlation between the time-variant digital signal amplitudes 76 and the time-variant modified digital target voltage amplitudes 102. As shown in FIG. 4B, the first curve 128 corresponds to a first slope m₁ (m₁=tan(θ₁)) and the second curve 130 corresponds to a second slope m₂ (m₂=tan(θ₂)). Given that θ₁>θ₂, the first slope m₁ is greater than the second slope m₂. In this regard, the second curve 130 has a reduced second slope m₂ relative to the first slope m₁. In this regard, the time-variant modified digital target voltage amplitudes 102 represented by the second curve 130 may be generated by applying a slope factor to the time-variant digital signal amplitudes 75 represented by the first curve 128. In a non-limiting example, the slope factor is less than 1. The first slope m₁ and a first intercept value associated with the first curve 128 may be applied by performing a linear fit of the first curve 128. The second slope m₂ may be generated by multiplying the first slope m₁ by the slope factor (m₂=m₁×slope factor). Subsequently, a second intercept value associated with the second curve 130 may be so determined to cause the first curve 128 and the second curve 130 to converge at a common digital amplitude ceiling 132. In this regard, the second curve 130 represents a number of variable voltage offsets V_(OFFSET-1)-V_(OFFSET-N) relative to the first curve 128. As such, the time-variant modified digital target voltage amplitudes 102 can be generated by adding the variable voltage offsets V_(OFFSET-1)-V_(OFFSET-N) to the time-variant digital target voltage amplitudes 100. Notably, the time-variant digital target voltage amplitudes 100 and the time-variant modified digital target voltage amplitudes 102 may conform to a common digital amplitude ceiling 132, which may be equal to 5.5 volts for example. It may also be possible to apply soft clipping to the time-variant digital target voltage amplitudes 100 and the time-variant modified digital target voltage amplitudes 102 in a region near the common digital amplitude ceiling 126 and/or in a region near zero.

FIG. 5 is a schematic diagram of an exemplary digital voltage processing circuit 94B configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit 58 of FIG. 2 as the digital voltage processing circuit 94. Common elements between FIGS. 3 and 5 are shown therein with common element numbers and will not be re-described herein.

The digital voltage processing circuit 94B includes gain adjustment circuitry 134, which can be activated in the high-bandwidth mode via the first control signal 90 and deactivated in the low-bandwidth mode via the second control signal 92. When activated, the gain adjustment circuitry 134 generates a respective voltage offset ΔV for each of the time-variant digital signal amplitudes 76. The gain adjustment circuitry 134 may generate the voltage offset ΔV as the constant voltage offset V_(OFFSET) of FIG. 4A or as the variable voltage offsets V_(OFFSET-1)-V_(OFFSET-N) of FIG. 4B for the time-variant digital signal amplitudes 76. When deactivated, the voltage adjustment circuitry 134 may generate the voltage offset ΔV as a zero voltage offset.

The digital voltage processing circuit 94B includes a combiner 136. The combiner 136 is configured to combine the respective voltage offset ΔV with each of the time-variant digital target voltage amplitudes 100 generated by the low-bandwidth LUT circuitry 116. In this regard, in the high-bandwidth mode, the combiner 136 may receive the respective voltage offset ΔV as a non-zero voltage offset. Accordingly, the combiner 136 outputs the digital target voltage signal 98 having the time-variant modified digital target voltage amplitudes 102. In contrast, in the low-bandwidth mode, the combiner 136 may receive the respective voltage offset ΔV as a zero voltage offset. Accordingly, the combiner 136 outputs the digital target voltage signal 98 having the time-variant digital target voltage amplitudes 100.

FIG. 6 is a schematic diagram of an exemplary digital voltage processing circuit 94C configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit 58 of FIG. 2 as the digital voltage processing circuit 94. Common elements between FIGS. 3 and 6 are shown therein with common element numbers and will not be re-described herein.

The digital voltage processing circuit 94C includes gain adjustment circuitry 138, which can be activated in the high-bandwidth mode via the first control signal 90 and deactivated in the low-bandwidth mode via the second control signal 92. When activated, the gain adjustment circuitry 138 generates a respective gain offset ΔG for each of the time-variant digital signal amplitudes 76. When deactivated, the gain adjustment circuitry 138 may generate the gain offset ΔG as a zero gain offset.

The digital voltage processing circuit 94C includes a gain mixer 140. The gain mixer 140 is configured to combine the respective gain offset ΔG with each of the time-variant digital signal amplitudes 76. In this regard, in the high-bandwidth mode, the gain mixer 140 may receive the respective gain offset ΔG as a non-zero gain offset. Accordingly, the gain mixer 140 outputs a number of time-variant modified digital signal amplitudes 142. In contrast, in the low-bandwidth mode, the gain mixer 140 may receive the respective gain offset ΔG as a zero gain offset. Accordingly, the gain mixer 140 outputs the time-variant digital signal amplitudes 76.

The digital voltage processing circuit 94C includes LUT circuitry 144. In the high-bandwidth mode, the LUT circuitry 144 generates the digital target voltage signal 98 corresponding to the time-variant modified digital target voltage amplitudes 102 that are formed based on the time-variant modified digital signal amplitudes 142. In the low-bandwidth mode, the LUT circuitry 144 generates the digital target voltage signal 98 corresponding to the time-variant digital target voltage amplitudes 100 that are formed based on the time-variant digital signal amplitudes 76.

FIG. 7 is a schematic diagram of an exemplary digital voltage processing circuit 94D configured according to another embodiment of the present disclosure and can be included in the ET amplifier circuit 58 of FIG. 2 as the digital voltage processing circuit 94. Common elements between FIGS. 6 and 7 are shown therein with common element numbers and will not be re-described herein.

In the digital voltage processing circuit 94D, the gain adjustment circuitry 138 is coupled to the mixer 110. When activated, the gain adjustment circuitry 138 generates a respective gain offset ΔG for each of the time-variant digital signal amplitudes 76. When deactivated, the gain adjustment circuitry 138 may generate the gain offset ΔG as a zero gain offset.

The mixer 110 is further configured to combine the respective gain offset ΔG with each of the time-variant digital signal amplitudes 76. In this regard, in the high-bandwidth mode, the mixer 110 may receive the respective gain offset ΔG as a non-zero gain offset. Accordingly, the mixer 110 outputs the time-variant modified digital signal amplitudes 142. In contrast, in the low-bandwidth mode, the mixer 110 may receive the respective gain offset ΔG as a zero gain offset. Accordingly, the mixer 110 outputs the time-variant digital signal amplitudes 76.

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow. 

What is claimed is:
 1. An envelope tracking (ET) amplifier circuit comprising: an ET voltage circuit configured to generate an ET modulated voltage corresponding to a time-variant voltage envelope; a signal processing circuit configured to generate a radio frequency (RF) signal corresponding to a time-variant signal envelope; an amplifier circuit configured to amplify the RF signal based on the ET modulated voltage; and a voltage processing circuit configured to operate in a low-bandwidth mode and a high-bandwidth mode; wherein the voltage processing circuit is further configured to cause the ET voltage circuit to modify the ET modulated voltage in the high-bandwidth mode to compensate for a temporal misalignment between the time-variant voltage envelope and the time-variant signal envelope at the amplifier circuit such that a linearity degradation caused by the temporal misalignment is reduced to a predetermined threshold.
 2. The ET amplifier circuit of claim 1 wherein the voltage processing circuit is further configured to not cause the ET voltage circuit to modify the ET modulated voltage in the low-bandwidth mode.
 3. The ET amplifier circuit of claim 1 wherein the voltage processing circuit is further configured to: operate in the low-bandwidth mode when the RF signal is less than or equal to 60 MHz bandwidth; and operate in the high-bandwidth mode when the RF signal is modulated greater than 60 MHz bandwidth.
 4. The ET amplifier circuit of claim 1 wherein the predetermined threshold corresponds to a predetermined adjacent channel leakage ratio (ACLR).
 5. The ET amplifier circuit of claim 1 wherein: the voltage processing circuit comprises: a digital voltage processing circuit configured to: generate a digital target voltage signal corresponding to a plurality of time-variant digital target voltage amplitudes in the low-bandwidth mode; and generate the digital target voltage signal corresponding to a plurality of time-variant modified digital target voltage amplitudes in the high-bandwidth mode; a digital-to-analog converter (DAC) configured to: convert the digital target voltage signal into a target voltage signal having a time-variant target voltage envelope formed based on the plurality of time-variant digital target voltage amplitudes in the low-bandwidth mode; and convert the digital target voltage signal into the target voltage signal having the time-variant target voltage envelope formed based on the plurality of time-variant modified digital target voltage amplitudes in the high-bandwidth mode; and the ET voltage circuit is further configured to generate the ET modulated voltage having the time-variant voltage envelope formed based on the time-variant target voltage envelope.
 6. The ET amplifier circuit of claim 5 wherein the signal processing circuit is further configured to: receive a digital signal corresponding to a plurality of time-variant digital signal amplitudes; and convert the digital signal into the RF signal having the time-variant signal envelope formed based on the plurality of time-variant digital signal amplitudes.
 7. The ET amplifier circuit of claim 6 wherein the digital voltage processing circuit comprises: a mixer configured to combine the plurality of time-variant digital signal amplitudes with a digital voltage reference signal to generate a digital target voltage reference signal corresponding to the plurality of time-variant digital signal amplitudes; low-bandwidth look-up table (LUT) circuitry configured to: receive the digital target voltage reference signal; and generate the digital target voltage signal having the plurality of time-variant digital target voltage amplitudes based on the plurality of time-variant digital signal amplitudes; and high-bandwidth LUT circuitry configured to: receive the digital target voltage reference signal; and generate the digital target voltage signal having the plurality of time-variant modified digital target voltage amplitudes based on the plurality of time-variant digital signal amplitudes.
 8. The ET amplifier circuit of claim 7 further comprising a multiplexer configured to: output the digital target voltage signal having the plurality of time-variant modified digital target voltage amplitudes in response to receiving a first control signal; and output the digital target voltage signal having the plurality of time-variant digital target voltage amplitudes in response to receiving a second control signal.
 9. The ET amplifier circuit of claim 7 wherein the high-bandwidth LUT circuitry is further configured to generate the plurality of time-variant modified digital target voltage amplitudes by adding a constant voltage offset to the plurality of time-variant digital target voltage amplitudes, respectively.
 10. The ET amplifier circuit of claim 7 wherein the high-bandwidth LUT circuitry is further configured to generate the plurality of time-variant modified digital target voltage amplitudes by adding a plurality of variable voltage offsets to the plurality of time-variant digital target voltage amplitudes, respectively.
 11. The ET amplifier circuit of claim 10 wherein: the plurality of time-variant digital target voltage amplitudes correspond to a first linear curve having a first slope; and the plurality of time-variant modified digital target voltage amplitudes correspond to a second linear curve having a second slope smaller than the first slope.
 12. The ET amplifier circuit of claim 11 wherein the first linear curve and the second linear curve converge at a common digital amplitude ceiling.
 13. The ET amplifier circuit of claim 6 wherein the digital voltage processing circuit comprises: a mixer configured to combine the plurality of time-variant digital signal amplitudes with a digital voltage reference signal to generate a digital target voltage reference signal corresponding to the plurality of time-variant digital signal amplitudes; low-bandwidth look-up table (LUT) circuitry configured to: receive the digital target voltage reference signal; and generate the plurality of time-variant digital target voltage amplitudes based on the plurality of time-variant digital signal amplitudes; and voltage adjustment circuitry configured to: receive the digital target voltage reference signal; and generate a respective voltage offset for each of the plurality of time-variant digital signal amplitudes.
 14. The ET amplifier circuit of claim 13 further comprising a combiner coupled to the low-bandwidth LUT circuitry and the voltage adjustment circuitry, the combiner is configured to: combine each of the plurality of time-variant digital target voltage amplitudes with the respective voltage offset to output the plurality of time-variant modified digital target voltage amplitudes in the high-bandwidth mode; and output the plurality of time-variant digital target voltage amplitudes in the low-bandwidth mode.
 15. The ET amplifier circuit of claim 14 wherein: the voltage adjustment circuitry is activated in the high-bandwidth mode such that the combiner receives the respective voltage offset as a non-zero voltage offset; and the voltage adjustment circuitry is deactivated in the low-bandwidth mode such that the combiner receives the respective voltage offset as a zero voltage offset.
 16. The ET amplifier circuit of claim 6 wherein the digital voltage processing circuit comprises: a mixer configured to combine the plurality of time-variant digital signal amplitudes with a digital voltage reference signal to generate a digital target voltage reference signal corresponding to the plurality of time-variant digital signal amplitudes; gain adjustment circuitry configured to: receive the digital target voltage reference signal; and generate a respective gain offset for each of the plurality of time-variant digital signal amplitudes; a gain mixer configured to: receive the digital target voltage reference signal; combine the respective gain offset with the plurality of time-variant digital signal amplitudes to generate a plurality of time-variant modified digital signal amplitudes in the high-bandwidth mode; and output the plurality of time-variant digital signal amplitudes in the low-bandwidth mode; and look-up table (LUT) circuitry configured to: generate the plurality of time-variant modified digital target voltage amplitudes in the high-bandwidth mode based on the plurality of time-variant modified digital signal amplitudes; and generate the plurality of time-variant digital target voltage amplitudes in the low-bandwidth mode based on the plurality of time-variant digital signal amplitudes.
 17. The ET amplifier circuit of claim 16 wherein: the gain adjustment circuitry is activated in the high-bandwidth mode such that the gain mixer receives the respective gain offset as a non-zero gain offset; and the gain adjustment circuitry is deactivated in the low-bandwidth mode such that the gain mixer receives the respective gain offset as a zero gain offset.
 18. The ET amplifier circuit of claim 6 wherein the digital voltage processing circuit comprises: a mixer configured to combine the plurality of time-variant digital signal amplitudes with a digital voltage reference signal to generate a digital target voltage reference signal corresponding to the plurality of time-variant digital signal amplitudes; gain adjustment circuitry configured to generate a respective gain offset for each of the plurality of time-variant digital signal amplitudes; the mixer further configured to: combine the respective gain offset with the plurality of time-variant digital signal amplitudes to generate a plurality of time-variant modified digital signal amplitudes in the high-bandwidth mode; and output the plurality of time-variant digital signal amplitudes in the low-bandwidth mode; and look-up table (LUT) circuitry configured to: generate the plurality of time-variant modified digital target voltage amplitudes in the high-bandwidth mode based on the plurality of time-variant modified digital signal amplitudes; and generate the plurality of time-variant digital target voltage amplitudes in the low-bandwidth mode based on the plurality of time-variant digital signal amplitudes.
 19. The ET amplifier circuit of claim 5 wherein the voltage processing circuit further comprises voltage memory digital pre-distortion (mDPD) circuitry configured to digitally pre-distort the digital target voltage signal to compensate for memory nonlinearity distortion in the ET voltage circuit.
 20. The ET amplifier circuit of claim 19 wherein the voltage processing circuit further comprises delay adjustment circuitry configured to reduce the temporal misalignment between the time-variant voltage envelope and the time-variant signal envelope.
 21. The ET amplifier circuit of claim 19 wherein the signal processing circuit comprises delay adjustment circuitry configured to reduce the temporal misalignment between the time-variant voltage envelope and the time-variant signal envelope.
 22. The ET amplifier circuit of claim 1 further comprising a control circuit configured to control the voltage processing circuit to cause the ET voltage circuit to modify the ET modulated voltage in the high-bandwidth mode. 